Not Applicable
1. Field of the Invention
The present invention relates to FETs (Field Effect Transistors), and more particularly to those with short, e.g., less than 50 nm, gate length.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
As CMOS technology becomes smaller, e.g., less than 50 nm gate length, it becomes more and more difficult to improve the short channel device performance and at the same time maintain acceptable values for off-state leakage current.
One technique for trying to achieve this is the halo technique wherein extra dopant implant regions are next to the source and drain extension regions. For this to work the junctions must be abrupt, see xe2x80x9cCMOS Devices below 0.1 nm: How High Will Performance Go?xe2x80x9d, by Y. Taur, et al., pp. 1-4. In particular, for sub 50 nm devices, not only the extension regions near the channel must be abrupt, i.e., less than 4 nm/decade, but the halo profile in proximity to the extension junction must be abrupt, i.e., less than 20 nm/decade. Most of the prior art for the halo formation used a general approach wherein halo dopants are implanted at an angle ranging from 0xc2x0 to 70xc2x0 into the channel region. This prior art varied either the dose, halo dopants, or angle of halo implants for improving the device performance. The article xe2x80x9cHalo Doping Effects in Submicron DI-LDD Device Designxe2x80x9d by Christopher Codella et al. pp. 230-233 describes the optimum halo doses for improving the threshold voltage and the punch-through device characteristics. Punch-through stoppers was also discussed in the U.S. Pat. No. 5,320,974 by Atsushi Hori et al. which is similar to the conventional halo arrangements. The article xe2x80x9cA 0.1 nm IHLATI (Indium Halo by Large Angle Tilt Implant) MOSFET for 1.0V Low Power Applicationxe2x80x9d by Young Jin Choi et al. described the use of indium halo and large angle tilt for indium halo implants for improving the short channel characteristics. Other articles are xe2x80x9cHigh Carrier Velocity and Reliability of Quarter-Micron SPI (Self-Aligned Pocket Implantation) MOSEFETsxe2x80x9d by A. Hori et al. and xe2x80x9cA 0.1-xcexcm CMOS Technology with Tilt-Implanted Punchthrough Stopper (TIPS)xe2x80x9d by T. Hori. None of the prior art focussed attention on improving the abruptness of the halo dopant profiles in the area next to the channel. In these prior art situations, the halo dopants would have suffered enhanced transient diffusion during extension junction and high thermal budget deep source/dran rapid thermal anneal (typically 1000xc2x0 C. for 5 seconds) . Consequently, these much degraded halos severely compromised their usefulness for improving the short channel device characteristics, and this is especially the case for device channel width below 50 nm. Thus all the prior art approaches provide no means to minimize transient enhanced diffusion of the halo dopants and hence cannot be used to create the abrupt super-halo ( less than 20 nm/decade) in the region next to the channel area.
It is therefore desirable to have an abrupt junction even after annealing.
An apparatus comprises a semiconductor substrate comprising at least one PN junction, dopant atoms disposed within said semiconductor substrate at said PN junction, and a diffusion barrier disposed adjacent at said PN junction.
A process comprises forming a semiconductor PN junction with dopant atoms thereat and forming a diffusion barrier adjacent at said junction.